When people spec out a motherboard, they look at its PCIe generation numbers, VRMs, chipset lanes, and connectivity. What almost nobody pays attention to, however, is PCIe bifurcation, despite it being one of the most transformative features the platform can support.
It's not one of the things that can boost your frame rates, affect your CPU or GPU performance, or make your setup look aesthetically pleasing. Instead, it affords you some added flexibility, which, if used wisely, can be used to support some devices with very useful features. Here's why you should know a little more about it.
What is PCIe bifurcation?
Understanding the basics
PCIe bifurcation is a process that lets you split an existing high-bandwidth PCIe slot on your motherboard into multiple PCIe links, enabling you to support multiple devices that can leverage them. For example, you can divide a PCIe x16 slot into multiples of eight or four, which means it can support the following configurations:
- x8 / x8
- x8 / x4 / x4
- x4 / x4 / x4 / x4
Each lane 'split' can behave like an independent PCIe connection if your board supports it. What's worth mentioning here is that it is fundamentally different from a PCIe switch or a hub. Since bifurcation occurs at the CPU and chipset levels, all devices enjoy lower latency and are not subject to bandwidth penalties.
While the feature is common in most high-end boards (such as Intel's Z series, AMD's X series, and HEDT variants), it's not unusual for mid-range boards like B550 and B650 models to feature it too.
PCIe bifurcation is not "plug-and-play". Even if you have a compatible motherboard that is capable of it, your system will default to treating every slot as a single device unless manually configured via BIOS.
Why is PCIe bifurcation useful?
You can make use of that spare slot
Bifurcation can be a great way to optimize your high-bandwidth slots and achieve a little extra flexibility. It allows you to run multiple high-speed devices without stepping down to slower chipset lanes. It's sort of like a "Swiss Army Knife" of motherboard features, allowing you to upgrade your setup laterally.
Say, you're looking for more storage for a creative workstation but aren't very keen on going back to SATA SSDs and the extra wire management they entail. Since most motherboards only offer a couple of M.2 slots, it's understandable if you're left needing a few more. Through an NVMe expansion card, you can add up to four drives slotted into a single x16 PCIe slot without losing the bandwidth on either.
The use cases aren't just limited to storage expansion either. Power users who run local LLMs or frequently dabble in AI workloads can leverage PCIe bifurcation to split a single slot across multiple GPUs using risers, which can maximize compute density without needing to make a jump to a workstation-class setup. It is, however, important to note which PCIe riser is compatible with your motherboard to ensure compatibility.
5 ways to make use of PCIe Bifurcation in your PC
PCIe bifurcation can open a ton of doors for your setup
How to check if your motherboard supports it
It's fairly simple and can be worth your while
Finding out whether your chipset supports bifurcation can be a little tricky to say the very least, but as with most tweaks surrounding the motherboard, the discovery starts in your BIOS settings.
To access it, you'd have to reboot your PC and enter BIOS/UEFI by holding the BIOS key for your board. From there, you should look for settings like "PCIe slot configuration" or "PCIEX16 bandwidth". Some older boards directly show lane split options like 8x/8x or x4/x4/x4. Manufacturers may or may not make it easy for you, since it's rarely labeled as "bifurcation" and tucked away in the advanced settings. I was pleasantly surprised to find it underneath the 'chipset' settings on an old Gigabyte Aorus Elite B450M motherboard.
You can also refer to your motherboard manual. If you put away the box, you can search for one online. Some boards only support bifurcation on the top slot (which, if you're using a discrete GPU, is likely fully occupied), meanwhile, some disable it when a GPU is installed or allow specific ways to split the slot. After these steps, if you're still unable to find it, it's probably not supported on your board or the specific slot you're targeting.
When in doubt, it's always a good idea to refer to your motherboard manual.
One of the most alluring aspects of owning a PC is the customizability that comes with it, granting you the ability to build a system that fits the needs of your workflow. PCIe bifurcation takes it a step forward, and it is definitely worth looking into if your motherboard supports it.
Modularity is a thing of beauty
One of the most alluring aspects of owning a PC is the customizability that comes with it, granting you the ability to build a system that fits the needs of your workflow. PCIe bifurcation takes it a step forward, and it is definitely worth looking into if your motherboard supports it. Your spare PCIe slot can give you the gift of some additional storage, added performance, or perhaps a combination of the two if you've got the right components, unlocking capabilities that usually come with a hefty price tag. While you may not need it today, just knowing that you have the option to retrofit a few more upgrades can serve you well tomorrow.